Field of the Invention
The present invention relates to a method for controlling a braking force of a brake according to velocity. More particularly, it relates to a method for controlling a braking force according to velocity, which can improve initial braking ability while braking, when a vehicle is driven both at a high speed and a low speed using different hydraulic maps in braking at a low speed and braking at a high speed of the vehicle.
Description of Related Art
When a vehicle being running is braked, a braking force is generated by matching hydraulic force on the basis of a pedal stroke and the braking force depends on a pedal ratio, the specifications of a booster and a master cylinder, the size of a caliper piston size, an effective braking radius of a disc, the friction coefficient of a friction member, the tire size, etc.
A simulator is used for reproduction of the behavior of a pedal to develop a brake-by-wire type of brake system and the braking force of the brake system is obtained by generating hydraulic pressure with a device that generates and controls hydraulic pressure on the basis of a map set by developers.
According to the standards for developing such a brake system, “stroke vs braking force” and “pedal effort vs braking force”, etc. are mapped to achieve a braking ability similar to those of vehicles actually equipped with the braking system.
The “stroke vs braking force” is obtained by mapping hydraulic pressure to ensure a braking ability, as shown in FIG. 1A, and the “stroke vs braking force” is obtained by mapping hydraulic pressure to ensure a braking ability, as shown in FIG. 1B.
It has been known that early deceleration has much influence on braking ability, and the part corresponding to jump-in force of a brake for good early deceleration can be achieved by mapping hydraulic pressure.
Drivers feel that braking response is improved and the braking ability increases when the early deceleration is increased, but when the early deceleration is too large, drivers may feel uncomfortable because they feel like the vehicle is suddenly braked, and the difference in feeing of deceleration in braking is associated with the vehicle speed at the beginning of braking.
That is, it feels like braking response is good, rather than it is sudden braking, even if the initial braking force is large at a high vehicle speed, but it feels like sudden braking, even under the same initial braking force, when a vehicle is braked at a low speed.
However, there is a problem in that when the hydraulic pressure for braking is too high, it feels like the braking force is too large in braking at a low speed (feels like sudden braking), and when the hydraulic pressure decreases to prevent it, it feels as if the initial braking force is small while braking at a low speed (feels as if early deceleration is delayed).
It is impossible to solve the problem unless the parts of a brake system are changed, so the initial braking force has been set around a middle level through trade-off at an adequate level.
On the other hand, since there is a BAS (Brake Assist System) function, it is possible to rapidly increase a braking force up to the level when an ABS operates, in rapid braking under an emergency while a vehicle runs, but a driver cannot adjust the braking force within the range of braking force at the level before the ABS operates. Further, since deceleration close to the level when the ABS operates is very large deceleration, there may be a possibility of a collision with the vehicle behind.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.